Characterization of the mitogenic response of murine CD5+ and conventional B lymphocytes to lipopolysaccharide

B1 cells produce nitric oxide in response to a series of toll-like receptor ligands

The effect of a series of toll-like receptor (TLR) ligands on the production of nitric oxide (NO) in mouse B1 cells was examined by using CD5(+) IgM(+) WEHI 231 cells. The stimulation with a series of TLR ligands, which were Pam3Csk4 for TLR1/2, poly I:C for TLR3, lipopolysaccharide (LPS) for TLR4, imiquimod for TLR7 and CpG DNA for TLR9, resulted in enhanced NO production via augmented expression of an inducible type of NO synthase (iNOS). LPS was most potent for the enhancement of NO production, followed by poly I:C and Pam3Csk4. Imiquimod and CpG DNA led to slight NO production. The LPS-induced NO production was dependent on MyD88-dependent pathway consisting of nuclear factor (NF)-kappaB and a series of mitogen-activated protein kinases (MAPKs). Further, it was also dependent on the MyD88-independent pathway consisting of toll-IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) and interferon regulatory factor (IRF)-3. Physiologic peritoneal B1 cells also produced NO via the iNOS expression in response to LPS. The immunological significance of TLR ligands-induced NO production in B1 cells is discussed.

Attenuated liver fibrosis in the absence of B cells

Analysis of mononuclear cells in the adult mouse liver revealed that B cells represent as much as half of the intrahepatic lymphocyte population. Intrahepatic B cells (IHB cells) are phenotypically similar to splenic B2 cells but express lower levels of CD23 and CD21 and higher levels of CD5. IHB cells proliferate as well as splenic B cells in response to anti-IgM and LPS stimulation in vitro. VDJ gene rearrangements in IHB cells contain insertions of N,P region nucleotides characteristic of B cells maturing in the adult bone marrow rather than in the fetal liver. To evaluate whether B cells can have an impact on liver pathology, we compared CCl4-induced fibrosis development in B cell-deficient and wild-type mice. CCl4 caused similar acute liver injury in mutant and wild-type mice. However, following 6 weeks of CCl4 treatment, histochemical analyses showed markedly reduced collagen deposition in B cell-deficient as compared with wild-type mice. By analyzing mice that have normal numbers of B cells but lack either T cells or immunoglobulin in the serum, we established that B cells have an impact on fibrosis in an antibody- and T cell-independent manner.